We have previously shown that patients with hypokalemia (e.g. "Bartter's syndrome", "familial hypokalemia", or psychogenic vomiting) have an increase in adrenergic nervous system function (increase in the urinary excretion of catecholamines and increase in plasma norepinephrine). To discern whether the increase in sympathoadrenal function is caused by the low potassium per se, we have now studied the effects of hypokalemia, induced by feeding a potassium-deficient diet, on adrenergic function in the intact and in the pithed rat. The results show that a low extracellular potassium concentration is a potent stimulus of adrenergic function. The decrease in potassium appears to interfer with the release of norepinephrine. In addition, we have gained evidence that hypokalemia may increase norepinephrine synthesis.